1. Field of the Invention
The present invention relates to a method for controlling thicknesses of layers formed by a depositing apparatus for fabricating semiconductor devices. More particularly, the present invention relates to a method for controlling thicknesses of layers based on rapid and accurate analyses of measured data using an operation module included in a host computer.
2. Description of the Related Art
Generally, the fabrication of semiconductor devices involves highly precise processes that require finely tuned precision equipment. Several pieces of precision equipment are typically employed in sequence and arranged on a semiconductor processing line. The operation of each piece of precision equipment on the line is closely monitored by operators to maintain and enhance the efficiency of the processing line. The processing line frequently includes a deposition apparatus for depositing a desired substance in a layer with a desired thickness on a semiconductor substrate.
As shown in FIG. 1, a conventional deposition apparatus 3 is disposed on a conventional processing line. When a lot 10 of workpieces, such as wafers, are introduced into the deposition equipment 3, the deposition equipment 3 performs a deposition process on the lot 10. The deposition equipment 3 is connected on-line to a host computer 1 through a deposition equipment server 5. An operator interface (O/I) 2, for example an operator interface personal computer (O/I PC), is also connected on-line to the host computer 1. An appropriate process setting, for example, a desired deposition time duration or a desired deposition temperature, is entered into the host computer 1 by the operator through the O/I 2. The operator selects the process setting to give a desired layer thickness. The process setting is rapidly downloaded into the deposition equipment 3 from the host computer 1 through the deposition equipment server 5. Then the deposition equipment 3 performs based on the process settings received and deposits the given substance in a layer of a certain thickness on the workpieces of each lot 10.
At the end of the deposition process, the lot 10 of workpieces with the deposited layer is introduced into the measuring equipment 4. The thickness of the actually deposited layer is measured by the measuring equipment 4 for each lot. The measured thicknesses constitute thickness data that are rapidly uploaded to the host computer 1 through the measuring equipment server 6, and are then transferred to the O/I 2 by the host computer 1, and displayed at the O/I 2. The operator can monitor the displayed thickness measurements and reset the process settings presently used by the deposition apparatus 3 to obtain more desirable values of thickness.
The deposition process is carried out in such a manner that a plurality of lots 10, for example, six lots, are grouped as a batch for the deposition apparatus 3. In an exemplary deposition process, a layer, such as a metal layer or an oxidation layer for a semiconductor device, are deposited on the lots. FIG. 2 is a schematic cross sectional view of a conventional deposition apparatus and shows a boat 101 which holds several lots introduced into the deposition apparatus 3, each lot at a different position in the boat 101. For example, A indicates a central position in the deposition apparatus 3, B indicates an upper position in the deposition apparatus 3, and C indicates a lower position in the apparatus 3. Typically, the temperatures in the upper and lower positions B and C in the deposition equipment 3 have lower temperatures than the central position A because of the effect of external air. As a result, the thicknesses of the deposited layers vary according to the position of the lot within the deposition equipment 3. FIG. 3 is a graph showing the variation of thicknesses of layers formed on lots 10 in a conventional deposition apparatus 3 versus positions of the lots within the apparatus 3.
The thicknesses of the deposited layers also vary from batch to batch. FIG. 4 is a graph of thicknesses of layers formed in lots by a conventional deposition equipment versus batch units of the lots. The deposition process is performed on a batch unit after a deposition time duration is set by the operator. As the deposition time settings are varied for the different batches, the average thickness of the deposited layers also varies. The distribution of the average thickness of the deposited layers on the lots in the batch according to the batch number is shown in FIG. 4.
Based on his experiences, the operator analyzes the measured thickness data displayed at the O/I 2 immediately after each batch is processed in the deposition equipment 3 to determine whether the deposition process has been performed properly, i.e., within design specification. Thereafter, based on the analyzed result, the operator may reset one or more of the apparatus settings, such as the deposition time or the deposition temperature, to more appropriate values to minimize the deviations from the design specification for layer thicknesses. Typically, the operator controls the differences in the average thicknesses of the respective batches by resetting the deposition time, and controls the differences in the thicknesses according to lot positions within the apparatus by resetting the deposition temperature.
However, such a conventional method for controlling thicknesses of layers deposited by the deposition equipment 3 suffers from several problems. First, the results of the analysis of the measured data depends primarily on a human operator's attention and understanding, which takes time and is not perfect. That is, human operator analysis has a finite error rate. Consequently, in the event that any error occurs, even accidently, the result may be a serious failure of the process.
Secondly, the results of the analysis of the measured data and the corrective settings determined thereby are variable according to which operator analyzes the data. That is, human operator analysis is subjective, not objective. As a result, the data analyses lacks consistency and production control of the products from the processing line may become difficult.
Thirdly, it is very difficult for an inexperienced operator to analyze the measured data. Accordingly, the analysis tasks may be concentrated on skilled operators. This may result in relatively costly analyses.
Finally, a human operator can only function at a finite speed, so the analysis time can not be substantially reduced from current analysis times. This can limit the productivity of the processing line.